IN VITRO INCORPORATION OF 3H-THYMIDINE, 3H-URIDINE, 3H-LEUCINE AND 3H-MELPHALAN BY PLASMACYTOMA PLASMA CELLS

Bone marrow plasma cells from fifteen cases of multiple myeloma, immunologically typed, were incubated with different tritiated compounds. The labelling index with tritiated thymidine is generally low, while the mean grain count is fairly normal in the active cells. The labelling index of ³H-uridine and ³H-leucine was very high, while the mean grain count per cell lies within the normal range. The results obtained with ³H-phenylalanine-mustard (melphalan), which is a drug used in the treatment of the plasmacytoma, show also incorporation values roughly comparable to those of ³H-leucine. The present data seem to support the clinical use of melphalan as a compound that is actively incorporated into the plasma cells of plasmacytoma although inhibition of protein synthesis due to specific binding to protein was not demonstrated.     

Short term 22Na+ and 42K+ uptake in intact, mid-vegetative plants

Spergularia marina (L.) Griseb. is. a rapidly growing, annual, coastal halophyte. Because of its small size, it is suitable for isotope studies of ion transport well beyond the seedling stage. The purpose of this report is to establish the similarities and differences between ²²Na⁺ and ⁴²K⁺ uptake in S. marina and in more commonly used mesophytic crop species. Vegetative plants were used 18 days after transfer to solution culture. Plants were grown either on Na⁺-free medium or on 0.2 × sea water. ²²Na⁺ uptake was linear with time for several hours. The rate was relatively insensitive to external concentration between 1 and 180 mol Na⁺ m?³, particularly in Na⁺-free plants. Transport to the shoot accounted for 40 to 70% of the total uptake, dependent on salinity but largely independent of time. ⁴²K⁺ uptake decreased with increasing salinity in Na⁺-free plants and increased in 0.2 × sea water plants. Both uptake and transport to the shoot were non-linear with time, upward concavity suggesting recovery from a manipulative and/or osmotic injury. Steady state root contents were compared with predicted contents based on cortical cell electrical potentials using the Nernst equation. Reasonable agreement was found in all cases except Na⁺ content of 0.2 × sea water plants, in which active efflux was indicated. Uptake studies conducted in the presence of chemical modifiers (dicyclohexylcarbodiimide, dinitrophenol and fusicoccin) showed responses of ⁴²K⁺ uptake as expected from studies on agronomic species, and implied the presence of a similar active uptake here despite the appearance of equilibrium. Active Na⁺ uptake was suggested at low Na⁺ levels. We conclude that S. marina is a promising experimental system combining the rapid nutrient acquisition strategy of agionomically important annuals with a high degree of salt tolerance.     

The Effect of Dichlorophenyldimethylurea on Light-Stimulated 22Na+, 42K+ and 86Rb+ Absorption in Different Tissues of Phaseolus vulgaris Leaves

The light-stimulated absorption of ⁸⁶Rb⁺ by Phaseolus vulgaris L. leaf slices was found to be sensitive to dichlorophenyldimethylurea in air as well as in nitrogen, whereas light-stimulated ²²Na⁺ absorption in nitrogen was not sensitive to this inhibitor. The absorption of ²²Na⁺ is not affected by light in air. The absorption of ⁴²K⁺ is enhanced by a dichlorophenyldimethylurea-insensitive light effect under anaerobic conditions and further increased by light in the absence of the inhibitor. Light-enhanced ⁴²K⁺ absorption in air was also inhibited by dichlorophenyldimethylurea. Previous work showed that light-stimulated ⁸⁶Rb⁺ and ⁴²K⁺ absorption by Phaseolus vulgaris leaf slices is restricted to the guard cells. The present results are discussed with reference to the effect of light on stomatal opening.     

Tracer studies of gas circulation in Nuphar: 18O2 and 14CO2 transport

The objective of this study was to investigate the behaviour of different legumes against salinity and water stress, thus trying to discover simultaneous adaptations to both stresses. The nitrogen fixation, transpiration, predawn leaf water potential, and stomatal response of Medicago sativa L. (cvs. Tierra de Campos and Aragon), Trifolium repens L. (cv. Aberystwyth S-184) and T. brachycalycinum Katzn. et Morley (= T. subterraneum L. cv. Clare) were compared at three levels of stress (0.05, 0.3 and 0.5 MPa of either NaCl or polyethylene glycol 6000) in nutrient solution. The plants were stressed for three days and then returned to control nutrient solution. The changes in the parameters analyzed were dependent on the proportion of stress treatments and the nature of the species, always being greater in plants from PEG than from NaCl solutions. Transfer of lucerne and subclover plants from NaCl at 0.05 MPa to a non-saline medium resulted in an increase of nitrogen fixation above the level of the non-salinized control plants, especially significant in lucerne. Analysis of possible inorganic impurities in commercial PEG suggest that such type of impurities are not responsible for the toxic effects reported. Plant damage resulting from PEG treatment was apparently due to penetrations of PEG (as determined qualitatively by using the tetraiodinebismuthic acid technique) or low-molecular organic impurities into the plant. – The results are discussed as part of the adaptation of the different species to salinity and water stress. The best performance was given by "Tierra de Campos".     

Acquisition and within-plant allocation of 13C and 15N in CO2-enriched Quercus robur plants

We assessed the effects of doubling atmospheric CO₂ concentration, [CO₂], on C and N allocation within pedunculate oak plants (Quercus robur L.) grown in containers under optimal water supply. A short-term dual ¹³CO₂ and ¹⁵NO₃^? labelling experiment was carried out when the plants had formed their third growing flush. The 22-week exposure to 700 μl l^?1 [CO₂] stimulated plant growth and biomass accumulation (+53% as compared with the 350 μl l^?1 [CO₂] treatment) but decreased the root/shoot biomass ratio (-23%) and specific leaf area (-18%). Moreover, there was an increase in net CO₂ assimilation rate (+37% on a leaf dry weight basis; +71% on a leaf area basis), and a decrease in both above- and below-ground CO₂ respiration rates (-32 and -26%, respectively, on a dry mass basis) under elevated [CO₂]. ¹³C acquisition, expressed on a plant mass basis or on a plant leaf area basis, was also markedly stimulated under elevated [CO₂] both after the 12-h ¹³CO₂ pulse phase and after the 60-h chase phase. Plant N content was increased under elevated CO₂ (+36%), but not enough to compensate for the increase in plant C content (+53%). Thus, the plant C/N ratio was increased (+13%) and plant N concentration was decreased (-11%). There was no effect of elevated [CO₂] on fine root-specific ¹⁵N uptake (amount of recently assimilated ¹⁵N per unit fine root dry mass), suggesting that modifications of plant N pools were merely linked to root size and not to root function. N concentration was decreased in the leaves of the first and second growing flushes and in the coarse roots, whereas it was unaffected by [CO₂] in the stem and in the actively growing organs (fine roots and leaves of the third growth flush). Furthermore, leaf N content per unit area was unaffected by [CO₂]. These results are consistent with the short-term optimization of N distribution within the plants with respect to growth and photosynthesis. Such an optimization might be achieved at the expense of the N pools in storage compartments (coarse roots, leaves of the first and second growth flushes). After the 60-h ¹³C chase phase, leaves of the first and second growth flushes were almost completely depleted in recent ¹³C under ambient [CO₂], whereas these leaves retained important amounts of recently assimilated ¹³C (carbohydrate reserves?) under elevated [CO₂].     

Natural 13C and 15N abundance of field-collected fungi and their ecological implications

The natural abundance of ¹³C and ¹⁵N was measured in basidiocarps of at least 115 species in 88 genera of ectomycorrhizal, wood-decomposing and litter-decomposing fungi from Japan and Malaysia. The natural abundance of ¹³C and ¹⁵N was also measured in leaves, litter, soil and wood from three different sites. ¹⁵N and ¹³C were enriched in ectomycorrhizal and wood-decomposing fungi, respectively, relative to their substrates. Ectomycorrhizal and wood-decomposing fungi could be distinguished on the basis of their δ¹³C and δ¹⁵N signatures. Although there was high variability in the isotopic composition of fungi, the following isotope- enrichment factors (ε, mean±SD) of the fungi relative to substrates were observed:
ε_{ectomycorrhizal fungi/litter} = 6.1±0.4‰¹⁵N
ε_{ectomycorrhizal fungi/wood} = 1.4±0.8‰¹³C
ε_{wood-decomposing fungi/wood} = −0.6±0.7‰¹⁵N
ε_{wood-decomposing fungi/wood} = 3.5±0.9‰¹³C
The basis of isotope fractionation in C metabolism from wood to wood-decomposing fungus is discussed.     

Comparison of 125I-Angiotensin III and 125I-Angiotensin II Binding to Rat Brain Membranes

The binding of 125I-angiotensin III (125I-ANG III) to rat brain membranes was examined and compared with that of 125I-angiotensin II (125I-ANG II). Degradation of each ligand, as monitored by HPLC, was effectively inhibited using fragments of ANG III and ANG II known to have little affinity for angiotensin binding sites. Three classes of 125I-ANG III-binding sites were observed based on affinity (KD = 0.13, 1.83, and 10.16 nM) and capacity (Bmax = 1.30, 18.41, and 67.2 fmol/mg protein, respectively). Two classes of 125I-ANG II-binding sites of high affinity (KD = 0.11 and 1.76 nM) and low capacity (Bmax = 1.03 and 18.86 fmol/mg protein, respectively) were also identified. Cross-displacement studies confirmed that the two highest-affinity 125I-ANG III-binding sites and the 125I-ANG II-binding sites were the same. On the other hand, the binding of 125I-ANG III to the low-affinity 125I-ANG III-binding site could not be inhibited with ANG II. These data imply that previously measured differences in the biological potency of cerebroventricularly applied ANG III and ANG II probably do not result from differential binding of these peptides to central angiotensin receptors.     

FATE OF THYMOCYTES: STUDIES WITH 125I-IODODEOXYURIDINE AND 3H-THYMIDINE IN MICE

Cortical thymocytes of young adult mice were labeled in situ with radioactive DNA precursors. As a result of cell emigration and cell death, total thymic radioactivity decreased within 8 days to 10% or less of that present on day 1. Accumulation of thymic migrants in peripheral lymphoid organs was estimated by computing the net thymus-derived radioactivity in these tissues. Thymic cell death was assessed by comparing values obtained with ¹²⁵I-UdR to those acquired with ³H-TdR. The results indicate that cortical thymocytes migrate to the spleen, mesenteric lymph node, femurs and intestine; nevertheless, only a small fraction of the activity originally present in the thymus was recovered in these organs; the vast majority of newly formed cortical thymocytes apparently die after a relatively short life span. Exclusive of the fraction which dies in situ, evidence for thymocyte death is seen in bone marrow; however, most migrants appear to terminate in the intestine.     

Natural abundance of 13C and 15N in C3 and C4 vegetation of southern Africa: patterns and implications

The mean annual rainfall in southern Africa is found to explain over half of the observed variance in the stable nitrogen (N) isotopic signatures of C₃ vegetation in southern Africa (r²=0.54, P<0.01). The inverse relationship between the stable N isotopic signatures of foliar samples from C₃ vegetation and long‐term southern African rainfall is found on a scale larger than previously observed. A modest relationship is found between stable carbon (C) isotopic signatures of C₃ vegetation and rainfall across the region (r²=0.20, P<0.01). No such relationship is found between stable C and N isotopic signatures of C₄ vegetation and rainfall. The explanation of the relationship between ¹⁵N in C₃ vegetation and the mean annual rainfall presented here is that nutrient availability varies inversely with water availability. This suggests that water‐limited systems in southern Africa are more open in terms of nutrient cycling and therefore the resulting natural abundance of foliar ¹⁵N in these systems is enriched. The use of this relationship may be of value to those researchers modeling both the dynamics of vegetation and biogeochemistry across this region. The use of the isotopic enrichment in C₃ vegetation as a function of rainfall may provide an insight into nutrient cycling across the semi‐arid and arid regions of southern Africa. This finding has implications for the study of global change, especially as it relates to vegetation responses to changing regional rainfall regimes over time.     

Photosynthetic 14CO2 fixation and [15N]-ammonia assimilation during UV-B radiation of Lithodesmium variabile

Uptake of [¹⁵N]-ammonia was more sensitive to UV-B exposure than the total ¹⁴CO₂ fixation rate of Lithodesmium variabile Takano. Short-term UV-B radiation (15 min) had practically no effect on the kinetics of [¹⁵N]-ammonia, whereas there was an effect on [¹⁴C]-bicarbonate uptake rate. A significant reduction was found after 30 and 60 min UV-B stress. The time course of photosynthetic uptake of ¹⁵NH₄Cl at several wavelengths was markedly depressed at shorter wavelengths (irradiation with WG 280). A short-term (11 min) exposure to ultraviolet radiation had no influence on the [¹⁴C]-labeled photosynthetic products. However, the [¹⁵N]-label of several amino acids and the ratio of [¹⁵N]-glutamine to [¹⁵N]-glutamic acid varied after irradiation with different ultraviolet wavebands. The results are discussed with reference to UV damage to the key enzymes of nitrogen metabolism.     

Intracellular Calcium Dynamics and Cellular Energetics in Ischemic NG108-15 Cells Studied by Concurrent 31P/19F and 23Na Double-Quantum Filtered NMR Spectroscopy

Abstract: The role of voltage-sensitive Ca²⁺ channels in mediating Ca²⁺ influx during ischemia was investigated in NG108-15 cells, a neuronal cell line that does not express glutamate-sensitive receptor-mediated Ca²⁺ channels. Concurrent ³¹P/¹⁹F and ²³Na double-quantum filtered (DQF) NMR spectra were used to monitor cellular energy status, intracellular [Ca²⁺] ([Ca²⁺]_i), and intracellular Na⁺ content in cells loaded with the calcium indicator 1,2-bis-(2-amino-5-fluorophenoxy)ethane-N,N,N′,N′-tetraacetic acid (5FBAPTA) during ischemia and reperfusion. Cells loaded with 5FBAPTA were indistinguishable from unloaded cells except for small immediate decreases in levels of phosphocreatine (PCr) and ATP. Ischemia induced a steady decrease in intracellular pH and PCr and ATP levels, and a steady increase in intracellular Na⁺ content; however, a substantial increase in [Ca²⁺]_i (about threefold) was seen only following marked impairment of cellular energy status, when PCr was undetectable and ATP content was reduced to 55% of control levels. A depolarization-induced increase in [Ca²⁺]_i could be completely blocked by 1 µM nifedipine, whereas up to 20 µM nifedipine had no effect on the increase in [Ca²⁺]_i seen during ischemia. These data demonstrate that voltage-gated Ca²⁺ channels do not mediate significant Ca²⁺ flux during ischemia in this cell line and suggest an important role for Ca²⁺_i stores, the Na⁺/Ca²⁺ antiporter, or other processes linked to cellular energy status in the increase in cytosolic Ca²⁺ level during ischemia.     

Soil 13C–15N dynamics in an N2-fixing clover system under long-term exposure to elevated atmospheric CO2

Reduced soil N availability under elevated CO₂ may limit the plant's capacity to increase photosynthesis and thus the potential for increased soil C input. Plant productivity and soil C input should be less constrained by available soil N in an N₂‐fixing system. We studied the effects of Trifolium repens (an N₂‐fixing legume) and Lolium perenne on soil N and C sequestration in response to 9 years of elevated CO₂ under FACE conditions. ¹⁵N‐labeled fertilizer was applied at a rate of 140 and 560 kg N ha^?1 yr^?1 and the CO₂ concentration was increased to 60 Pa pCO₂ using ¹³C‐depleted CO₂. The total soil C content was unaffected by elevated CO₂, species and rate of ¹⁵N fertilization. However, under elevated CO₂, the total amount of newly sequestered soil C was significantly higher under T. repens than under L. perenne. The fraction of fertilizer‐N (f_N) of the total soil N pool was significantly lower under T. repens than under L. perenne. The rate of N fertilization, but not elevated CO₂, had a significant effect on f_N values of the total soil N pool. The fractions of newly sequestered C (f_C) differed strongly among intra‐aggregate soil organic matter fractions, but were unaffected by plant species and the rate of N fertilization. Under elevated CO₂, the ratio of fertilizer‐N per unit of new C decreased under T. repens compared with L. perenne. The L. perenne system sequestered more ¹⁵N fertilizer than T. repens: 179 vs. 101 kg N ha^?1 for the low rate of N fertilization and 393 vs. 319 kg N ha^?1 for the high N‐fertilization rate. As the loss of fertilizer‐¹⁵N contributed to the ¹⁵N‐isotope dilution under T. repens, the input of fixed N into the soil could not be estimated. Although N₂ fixation was an important source of N in the T. repens system, there was no significant increase in total soil C compared with a non‐N₂‐fixing L. perenne system. This suggests that N₂ fixation and the availability of N are not the main factors controlling soil C sequestration in a T. repens system.     

Carbon Isotope Ratios (13C/12C) in Fractions of Field-Grown Grape

The carbon isotope ratio (δ¹³C%) in leaves and berries of Vitis vinifera L. was determined during the fruiting season. The δ¹³C was from ?24.6 to ?26.3 in total leaf tissue, while it is from ?22.7 to ?24.3 in the aqueous extract of leaves. The δ¹³C in the berries was more stable, around ?24, with no change during ripening. Malic and tartaric acid, isolated from the berries at the onset of ripening, showed a δ¹³C of ?23.5 and ?23.0 respectively. It was concluded that malic acid accumulated in the berries at the onset of ripening is not formed directly through β-carboxylation.     

Brain Transfer Coefficients for 67Ga: Comparison to 55Fe and Effect of Calcium Deficiency

The transfer coefficients (Kin) for the uptake of gallium-67 (67Ga) into brain and CSF were determined in unanesthetized male Fischer-344 rats fed either a normal or a low-Ca diet. Kin for 67Ga was also compared with transfer coefficients for the uptake of iron-55 (55Fe) and 125I-albumin in control animals. The value of CSF 67Ga Kin was 3 x 10(-7) ml.g-1.s-1 and was 50% larger in low-Ca animals. Brain regional Kin values for 67Ga were 3-9 x 10(-7) ml.g-1.s-1 with no differences in Kin between normal and low-Ca rats. CSF Kin values for 55Fe were 40% and those for albumin were 15% of Kin for 67Ga. For brain, Kin values for 55Fe were 15-40% smaller than for 67Ga, but for albumin the Kin values were 85% less than for 67Ga. 67Ga was found to be 99% bound to plasma proteins, whereas 55Fe was 99.9% bound. The results indicate that metals that are primarily bound to transferrin enter the CSF and brain very slowly. Uptake of both metals was faster than albumin, which may indicate that metal bound to small chelates contributes significantly to brain uptake. In addition, Ca deficiency does not enhance entry of Ga into the brain.     

Correlating δ13C and δ18O in cellulose of trees

We measured the carbon and oxygen isotopic composition of stem cellulose of Pinus sylvestris, Picea abies, Fagus sylvatica and Fraxinus excelsior. Several sites along a transect of a small valley in Switzerland were selected which differ in soil moisture conditions. At every site, six trees per species were sampled, and a sample representing a mean value for the period from 1940 to 1990 was analysed. For all species, the mean site δ¹³C and δ¹⁸O of stem cellulose are related to the soil moisture availability, whereby higher isotope ratios are found at drier sites. This result is consistent with isotope fractionation models when assuming enhanced stomatal resistance (thus higher δ¹³C of incorporated carbon) and increased oxygen isotope enrichment in the leaf water (thus higher δ¹⁸O) at the dry sites. δ¹⁸ O-δ¹³C plots reveal a linear relationship between the carbon and oxygen isotopes in cellulose. To interpret this relationship we developed an equation which combines the above-mentioned fractionation models. An important new parameter is the degree to which the leaf water enrichment is reflected in the stem cellulose. In the combined model the slope of the δ¹⁸O-δ¹³C plot is related to the sensitivity of the p_i/p_a of a plant to changing relative humidity.     

13C and 15N in microarthropods reveal little response of Douglas-fir ecosystems to climate change

Understanding ecosystem carbon (C) and nitrogen (N) cycling under global change requires experiments maintaining natural interactions among soil structure, soil communities, nutrient availability, and plant growth. In model Douglas-fir ecosystems maintained for five growing seasons, elevated temperature and carbon dioxide (CO₂) increased photosynthesis and increased C storage belowground but not aboveground. We hypothesized that interactions between N cycling and C fluxes through two main groups of microbes, mycorrhizal fungi (symbiotic with plants) and saprotrophic fungi (free-living), mediated ecosystem C storage. To quantify proportions of mycorrhizal and saprotrophic fungi, we measured stable isotopes in fungivorous microarthropods that efficiently censused the fungal community. Fungivorous microarthropods consumed on average 35% mycorrhizal fungi and 65% saprotrophic fungi. Elevated temperature decreased C flux through mycorrhizal fungi by 7%, whereas elevated CO₂ increased it by 4%. The dietary proportion of mycorrhizal fungi correlated across treatments with total plant biomass (n= 4, r²= 0.96, P= 0.021), but not with root biomass. This suggests that belowground allocation increased with increasing plant biomass, but that mycorrhizal fungi were stronger sinks for recent photosynthate than roots. Low N content of needles (0.8–1.1%) and A horizon soil (0.11%) coupled with high C : N ratios of A horizon soil (25–26) and litter (36–48) indicated severe N limitation. Elevated temperature treatments increased the saprotrophic decomposition of litter and lowered litter C : N ratios. Because of low N availability of this litter, its decomposition presumably increased N immobilization belowground, thereby restricting soil N availability for both mycorrhizal fungi and plant growth. Although increased photosynthesis with elevated CO₂ increased allocation of C to ectomycorrhizal fungi, it did not benefit plant N status. Most N for plants and soil storage was derived from litter decomposition. N sequestration by mycorrhizal fungi and limited N release during litter decomposition by saprotrophic fungi restricted N supply to plants, thereby constraining plant growth response to the different treatments.